Modern gas turbine engines may employ an annular combustor arrangement wherein a single combustion chamber is defined by an inner liner, a concentric outer liner, and an annular combustor head located at the upstream end of the combustion chamber with respect to the overall working fluid flow. One configuration of combustor head includes a generally torroidal shaped plenum volume defined by an upstream dome portion which further includes an opening for receiving a flow of compressed, relatively cool air, and a downstream bulkhead which also defines the upstream end of the annular combustion chamber, spanning the radial gap between the inner and outer combustor liners. The bulkhead also includes a plurality of openings, distributed circumferentially and aligned with the openings in the combustor head dome portion, for receiving a corresponding plurality of fuel nozzles discharging liquid or gaseous fuel into the combustion chamber. This type of combustor arrangement is generally well known, illustrated, for example., in U.S. Pat. No. 4,686,823.
As can easily be appreciated, the combustor head and liners encompass the highest temperature region of the engine, with gas temperatures reaching up to 2,000 F. (1,100 C.) and higher. The presence of the high temperature combustion reaction in the confined combustor volume requires protection of the surrounding structure, i.e., the inner and outer liner and the upstream bulkhead, so as to avoid over temperature of the adjacent engine structure which would require premature replacement or refurbishment.
With specific regard to the bulkhead, prior art methods of protecting this structure from the combustion reaction occurring immediately downstream within the interior of the combustor have included an enlarged protective flange secured to a guide bushing surrounding each individual fuel nozzle which extends parallel to the bulkhead for a distance and which directs a film of cooling air received from the combustor head plenum volume over the bulkhead surface. Drawbacks associated with this prior art method include a lack of uniformity in the protection achieved by the cooling air flow discharged at the edges of the nozzle guide flange, as well as a lack of protection from radiation heat flux from the combustion reaction through the film of cooling air to the bulkhead surface.
What is required is a positive, effective method of providing thermal protection to the combustion reaction facing side of the combustor bulkhead.